Early IS research on satisfaction investigated system characteristics affecting end-user satisfaction, relying mostly on the IS success model. More recent research, on the other hand, studied satisfaction formation in the context of web-based products and services, using the disconfirmation theory. The IS context, however, is different from the marketing context where the theory was originally developed. One important difference is the novelty effect associated with the constant and rapid advancement of information technology. Previous satisfaction studies did not account for the dynamic nature of satisfaction and the changeability of its determinants. Such variability may be more salient in the IS context due to the novelty effect. In this paper, we develop, operationalize and empirically test a model for explaining/predicting satisfaction with Internet-based services at adoption and post-adoption stages. We argue and empirically demonstrate the need to consider the evolutionary nature of satisfaction and the variability of its determinants. Our results show that desires and expectations are both important factors that need to be considered simultaneously in explaining satisfaction at adoption. The role of desires, however, diminishes significantly in the post-adoption stage. The results also show no significant relationship between post-adoption satisfaction and satisfaction at adoption. The augmented disconfirmation model resulting from this study constitutes an important step towards the development of an IS satisfaction theory that accounts for the evolution of satisfaction over adoption stages.